#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define rep1(i,n) for(int i=1;i<=(int)(n);i++)
#define all(c) c.begin(),c.end()
#define pb push_back
#define fs first
#define sc second
#define show(x) cout << #x << " = " << x << endl
#define chmin(x,y) x=min(x,y)
#define chmax(x,y) x=max(x,y)
using namespace std;
typedef long long ll;
const ll ccc=200000;
bool prime[ccc+1];
vector<ll> pr;
void makeprime(){
	ll i,j;
	for(i=2;i<=ccc;i++) prime[i]=true;
	for(i=2;i*i<=ccc;i++) if(prime[i]) for(j=2;j*i<=ccc;j++) prime[j*i]=false;
	for(i=2;i<=ccc;i++) if(prime[i]) pr.push_back(i);
}
int cnt(int x){
	int s=0;
	while(x){
		s+=x%10;
		x/=10;
	}
	if(s<10) return s;
	return cnt(s);
}
int main(){
	makeprime();
	int a,b;
	cin>>a>>b;
	vector<int> ps,_;
	for(int p:pr) if(a<=p&&p<=b) ps.pb(cnt(p)),_.pb(p);
	int mx=0,id=0;
	rep(i,ps.size()){
		bool x[50]={};
		int e=0;
		for(int j=i;j<ps.size();j++,e++){
			if(x[ps[j]]) break;
			x[ps[j]]=1;
		}
		if(mx<=e){
			mx=e;
			id=_[i];
		}
	}
	cout<<id<<endl;
}